Steam generator blowdown apparatus

ABSTRACT

Removal of suspended particulate material in the secondary liquid circulated through a vapor generator of the shell and tube type is effected by the arrangement in the shell interior of baffle means defining a settling chamber therein. The baffle means is operative to retard the flow of secondary liquid and to effect an abrupt change in its direction of flow through the settling chamber whereby the suspended particles are caused to gravitate to the bottom thereof. Continuous or periodic flushing of the settling chamber is effected through a perforated blowdown pipe.

United States Patent Cassell Nov. 4, 1975 STEAM GENERATOR BLOWDOWN 3,139,070 6/1964 Sprague et al 122/34 APPARATUS 3,576,179 4/1971 Romanos 122/32 Inventor: Don Stuart Cassell, Chattanooga,

Tenn.

Assignee: Combustion Engineering, Inc.,

Windsor, Conn.

Filed: July 29, 1974 Appl. No.: 492,646

US. Cl. 122/32; 122/34; 122/381; 122/382 Int. Cl. F22b 37/54 Field of Search 122/32, 33, 34, 379, 381, 122/382 References Cited UNITED STATES PATENTS 12/1963 Sprague 122/34 Primary Examiner-Kenneth W. Sprague 57 ABSTRACT Removal of suspended particulate material in the secondary liquid circulated through a vapor generator of the shell and tube type is effected by the arrangement in the shell interior of bafile means defining a settling chamber therein. The bafile means is operative to retard the flow of secondary liquid and to effect an abrupt change in its direction of flow through the settling chamber whereby the suspended particles are caused to gravitate to the bottom thereof. Continuous or periodic flushing of the settling chamber is effected through a perforated blowdown pipe.

9 Claims, 4 Drawing Figures US. Patent Nov. 4, 1975 Sheet 1 of2 3,916,844

6 r 5 w Vi all/vl/l/l/iz/l/ll/ I I I I I f!!! US. Patent Nov. 4, 1975 Sheet 2 of 2 STEAM GENERATOR BLOWDOWN APPARATUS BACKGROUND OF THF. DISCLOSURE The present invention relates in general to vapor generators of the shell and tube type wherein vaporizable liquid, termed the secondary liquid, is transformed into vapor by passing it in heat exchange relation with the high temperature primary fluid that is conducted through the tubes. Vapor generators of this type characteristically employ a bundle of tubes, either of the inverted U-type in which both ends of each tube are connected to a single tube sheet or of the straight type in which the tubes are connected at their opposite ends to a pair of axially spaced tube sheets. The units operate with a body of secondary liquid maintained at a predetermined level in a downcomer annulus and a riser pas sage with circulation of the liquid between the two sections being maintained by the thermal syphonic action created by the difference in densities between the liquid bodies in the respective sections.

Conventionally. the secondary liquid flow through vapor generators of the described type is such that the liquid from the down-comer annulus enters the riser passage from its periphery and must turn and flow upwardly therethrough. This flow pattern creates a region of relatively stagnant flow in the lower part of the riser passage within which any suspended particles entrained in the secondary liquid, such as metal oxides or scaleforming calcium, may be permitted to settle thereby forming sediment deposits. Such deposits, if not removed. may cover the tube and tube sheet surfaces thereby operating to reduce the amount of heat transfer area provided thereby. Additionally, sediment deposits provide a convenient medium for the concentration of corrosive impurities, such as chloride salts, or

the like, which can attack the tube material and may result in tube failure thereby requiring shutdown of the plant.

Although the removal of sediment deposits has traditionally been provided by blowdown procedures in which the affected area receives a periodic or continuous flushing with relatively high velocity fluid, such procedures have become increasingly difficult as the capacity of shell and tube type vapor generators has increased. Increased unit capacities require a greater number of tubes disposed within the shell and. because of the desire to maintain the vapor generator shell as small as possible, there has been a tendency to accommodate the increased number of tubes by placing the tubes on closer spacing. Thus, blowdown is impeded since space is no longer available to accommodate the piping required to adequately flush all potentially affected regions of the tube bundle. To remove rows of tubes in order to accommodate additional blowdown piping is uneconomic because of the resultant loss of heat transfer area.

It is to the solution of such problems that the present invention is directed.

SUMMARY OF THE INVENTION ception of secondary liquid flowing within the unit and defines a flow path in which the secondry liquid underameter lower shell portion and a conical transition member interconnecting the two, in accordance with an aspect of the invention the baffle plate is conveniently disposed to cooperate with the transition member in defining the settling chamber. It should be understood, however, that the invention is equally applicable to shell and tube vapor generators having other shell configurations.

For a better understanding of the invention, its operating advantages and the specific objects obtained by its use. reference should be made to the accompanying drawings and description which relate to a. preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a vertical section of a typical shell and tube vapor generator equipped with apparatus of the present invention;

FIG. 2 is an enlarged partial vertical section of the vapor generator of FIG. I illustrating the settling cha n} her of the present invention in greater detail;

FIG. 3 is a plan section taken along line 3-3 of FIG. 2; and

FIG. 4 is an enlarged partial vertical section of an alternative form of the settling chamber of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I of the drawings, there is shown a shell and tube type vapor generator It) incorporating the present invention. It comprises a vertically elongated pressure vessel defined by a lower cylindrical shell section 12 and a larger diameter, upper cylindrical shell section 14, the latter being integrally connected with the former by means of a frustoconical transition member l6. The ends of the vessel are closed, at the bottom by means of hemispherically for med closure head land at the top by a dome-shaped; cover 20 containing a vapor outlet nozzle 22. The interior of the pressure vessel contains a plurality of annular baffles 24, 26 and 28, baffle 24 being a cylindrical shroud extending in coaxially spaced relation from the wall of the lower shell 12 to cooperate therewith in forming an inner riser passage 30 and an outer, annular downcomer passage 32. The lower end of the vessel interior is closed by tube sheet 34 disposed between the lower end of shell 12 and the lower closure head 18. The tube sheet 34 extends transversely of the vessel axis and connects at its periphery between the shell .12 and closure head 18. The tube sheet 34 contains a plurality of tube openings adapted to fixedly receive the ends of inverted U- shaped heat transfer tubes 38 that form a longitudinally extending tube bundle 40 substantially' filling the riser passage 30. The tube ends are open and extend through the tube sheet to place the tubes 38 in fluid communication with a heating fluid chamber that occupies that region of the vessel enclosed between the closure head 18 and the tube sheet 34 and which is divided into inlet and outlet portions 44 and 46, respectively, by means shown-)bymeans'of inlet and outletfnozzles 50,and $2, v

respectively, that :communicate with the respective chamberportions 44 and 46 and thereby effect circulation of heating fluid through the tubes-38.

-,I'Feedwate r= is"'; supplied to the unit-through an inlet nozzle'54that is shownpenetrating thenupper shell 14. A-"ring -h'eader 56 connects with, the-nozzle .'54,and serves to distribute feedwater passedthrough=the nozw, zle about-the circumference of thedowncomer passage, SZdischarging into the passage by means of downwardly-directed 'discharge'ports 58. Flow of feedwa'ter fromi thedowncomer passage 32 into the'riser passage 30iseffected by thevertically spaced relationship thatexists between the lower end of the cylindrical baffle plate 24 and theupper surface of tube sheet 34."Within the'riser passage the'feedwater 'is caused -to flow inheat exchange' relation' with the tubes 38 where 'heat is extracted' frorn the heating-fluid circulated therethrough to cause some of the feedwaterv to be-transformed into vapor; These-created vapor-liquid mixture flows to the upper region of the vapor generation chamber formed as a mixture collection chamber indicated as 60. From the r'nixture collection chamber 60 the flowing mixture is passedto vapor-liquid separator apparatus',-a'rnultiplicity o f' such separators indicated as 62 bein mounted upon baffle plate 28 and communicating with the char nberfip by means of 'openings61--'providedin the baffle. The separators 62 may be ofany well known -construction,5those shown being of the centrifugal type and area'rranged todisch'arge separated liquid downwa'rdly upon thebaffle plate 28 frdnf'whence it is-"returned tofthe downcomer. passage- 32 to be mixed with the incoming feedwater, and recircuIated through the unit. The separated vapor, on the other hand, is disjchargedfrorn the separators62 in the upward direction for discharge ofzthe vapor outlet noz zle' 22 from .-whence .it is jconductedt oa point of use. According to the present invention an annular baffle i s ,provided in the upperregi'on of the downcomer passage 32. The baffle 64 is concentrically space'd be- .tweenithe cylindrical shroud 24 and the interior surface of the pressure-shell. As shown, the baffle 64'i's prefera-; .bly disposed adjacent the transition member'16 to cooperate therewith in defining a settling chamber 66.

T.he lower-end of the baffle plate 64 is sealedly at- -;tached, as by means of welding to the juncture of the :Itransition member 16 and the lower shell section 1 2. thereby. forming the closed bottom of the chamber .At'itsupper end the baffle plate 64 possessesan'iout- 1 turned flange 68 intended to prevent flow of secondary liq'uid directly into the lower regionof the downcomer passage 32. The end edge of .the flange is disposed in close concentric spacingwith respect to the adjacent surface of the shroud 24 in order to accommodate thermally induced relative movements between the shroud and the shell. 1 v. a Adjacent the flange 68 the baffle plate defines aninletopening, indicated as 70, to the settling chamber 66. As shown, this opening is disposed below the discharge ports 58- of the feedwater inlet header 56 whereby'the secondary liquidadrnitted to theisettling chamber 66is a mixture ,ofithe fresh, incoming feedww 1 ter and separated liquid from the separatorsv62, the lat- -t'er being 'recirculated through the unit.

of a diametral plate 48, The heating fluid chamber 1;; ,T,

,baffle plate; i mpe'rforate 'overa principle portion of its lengthftdren'der' thesettling chamber 66 a reg'ioniof relatively-low liquidvelocity.: Adjacent its upper end ,'however, the plate is provided with a plurality of openings 72 which'esltablish fluid communication between these ttlingcharnber and the remainder of the downcomer passage 3 2." B y means'of this arrangement thesecondary liquidenteringthe settling chamber, in addition to having' itsflow velocity reduced, is also caused to undergo an abrupt reversal of direction as shown by thear rows 74 whereby entrained particulate material isre'movedfrom the'flo w streamby gravity and falls as sediment to the bottom of thecham-ber.

An annular"blowdown pipe 76' is disposed in the lower" regionof the settling ch amber'66. The pipe is perforated, as 51:78, along its length and'co'mmunicates with: the exterior'ofthe pressu r elshell' through blowdown nozzle 80 is as shownin FIG. 3, T- connected to the pipe. Means (not'shown) connect with the blowdown nozzle' 80 whereby blowdown of the removed particulate material can be effected on either a continuous or'a periodic basis.

n In FIG 4 of the drawing there is illustrated an alternative form of the invention in which the perforated baf fleplate j64of the ern bodiment'is replaced-in. thesettl ing chamber 66 byabaffle arrangement com prising members 82 and 84 which define a tortuous fluid: path between the se'"ttling "chamber and the re mainder of the fdo'wncomer passage3 2. Member '82 is upper end edge of the member 82 and telescopically encloses the amete define a fluid path by .-means of which the flowing secondary liquid is caused to undergo an abrupt change of direction prior to exiting the settling chamber 66 whereby to induce gravitational removal of entrained particulate material for discharge through blowdown pipe 76 in a mannersimilar to that effected by thearrangement shown in FIG. 1.

It will be appreciated; that apparatus as'hereindescribed provides ajcohvenient solution'l'to the problem of removing sedimefit forrningparticulate material from the secondary 'liq'uid tha't is circulated through J shell and tube vapor generators. Because the arrangemerit requires'no blowdown piping within 'thetinterior of the tube bundle, spaces thatcould only be produced parting from to shell an by the 'removal'of heat exchange tubes are not required. Moreover, because the settling chamber and its attendant blowdown pip'ingis locatedinthe dow'ncomer passage remote from the tubebundle no:heat

transfer surface is obstructed by the'blowdown apparatus. This, of course, enables more effective use of :the heating surface provided, by the tube. bundle.

While the preferred embodiment of the'present in- ,ven tio n. been described herein, it should be understood'that thedescription is merely illustrative and that variations and "modifications can be'made without den the spirit and scope of the inventionrFor example, the invention is not limited in its application e' vapor generators employing inverted U-tubes as in the described embodiment. The invention can be equally applied within the downcomer passage of vapor generators of the straight tube type.

What is sought to be protected herein is as recited in the appended claims.

What is claimed is:

1. In a shell and tube heat exchanger for the generation of vapor by the indirect transfer of heat from a heating fluid to a secondary liquid including a pressure shell having a transverse tube sheet defining a vapor generating region enclosing a bundle of heat exchange tubes emanating from said tube sheet, means for passing heating fluid through said tubes and means for circulating said secondary liquid through said vapor generating region exteriorly of said tubes, the improvement comprising means for the removal of suspended particulate material from said circulating secondary liquid, said means including:

a. baffle means defining a settling chamber forming a low liquid flow velocity region within the interior of said pressure shell;

b. said settling chamber having an opening for the reception of secondary liquid flowing within said vapor generating region and defining a flow path in which said secondary liquid undergoes an abrupt change of direction; and

c. a blowdown pipe operatively disposed in said set tling chamber and communicating with the exterior of said pressure shell for the discharge of settled particulate material from said settling chamber.

2. The organization according to claim 1 in which said heat exchanger includes a generally cylindrical baffle enclosing said bundle of heat exchange tubes in circumferentially spaced relation from the interior surface of said pressure shell to define an axial riser passage and an annular downcomer passage and said settling chamber is disposed in said downcomer passage.

3. The organization according to claim 2 in which said secondary liquid circulating means includes feedwater inlet means communicating with said downcomer passage upstream in the secondary liquid flow sense from said settling chamber.

4. The organization according to claim 2 in which said baffle means includes a substantially cylindrical plate concentrically spaced between said cylindrical baffle and the interior surface of said pressure shell defining an annular settling chamber about said downcomer passage, said plate being imperforate at least over a substantial portion of its length.

5. The organization of claim 4 in which said baffle plate includes an out-turned flange disposed adjacent the inlet opening of said settling chamber, said flange having an end surface in closely spaced concentric relation to said cylindrical baffle, and means forming perforations in said baffle plate adjacent said flange.

6. The organization of claim 4 in which said pressure shell includes an enlarged diameter upper shell portion and a reduced diameter lower shell portion, a conical transistion member connecting said shell portions, said baffle plate cooperating with the internal surface of said transition member to form said settling chamber.

7. The organization of claim 6 in which the lower end of said baffle plate is sealedly connected to said pressure shell at the juncture of said transition member and said lower shell portion.

8. The organization of claim 4 in which said cylindrical plate is attached to said pressure shell and including a second annular member attached to said cylindrical baffle in concentrically spaced relation to said cylindrical plate and cooperating therewith to define a tortuous fluid path between said settling chamber and said downcomer passage.

9. The organization of claim 4 in which said second annular member is angular in section and telescopically encloses said cylindrical plate. 

1. In a shell and tube heat exchanger for the generation of vapor by the indirect transfer of heat from a heating fluid to a secondary liquid including a pressure shell having a transverse tube sheet defining a vapor generating region enclosing a bundle of heat exchange tubes emanating from said tube sheet, means for passing heating fluid through said tubes and means for circulating said secondary liquid through said vapor generating region exteriorly of said tubes, the improvement comprising means for the removal of suspended particulate material from said circulating secondary liquid, said means including: a. baffle means defining a settling chamber forming a low liquid flow velocity region within the interior of said pressure shell; b. said settling chamber having an opening for the reception of secondary liquid flowing within said vapor generating region and defining a flow path in which said secondary liquid undergoes an abrupt change of direction; and c. a blowdown pipe operatively disposed in said settling chamber and communicating with the exterior of said pressure shell for the discharge of settled particulate material from said settliNg chamber.
 2. The organization according to claim 1 in which said heat exchanger includes a generally cylindrical baffle enclosing said bundle of heat exchange tubes in circumferentially spaced relation from the interior surface of said pressure shell to define an axial riser passage and an annular downcomer passage and said settling chamber is disposed in said downcomer passage.
 3. The organization according to claim 2 in which said secondary liquid circulating means includes feedwater inlet means communicating with said downcomer passage upstream in the secondary liquid flow sense from said settling chamber.
 4. The organization according to claim 2 in which said baffle means includes a substantially cylindrical plate concentrically spaced between said cylindrical baffle and the interior surface of said pressure shell defining an annular settling chamber about said downcomer passage, said plate being imperforate at least over a substantial portion of its length.
 5. The organization of claim 4 in which said baffle plate includes an out-turned flange disposed adjacent the inlet opening of said settling chamber, said flange having an end surface in closely spaced concentric relation to said cylindrical baffle, and means forming perforations in said baffle plate adjacent said flange.
 6. The organization of claim 4 in which said pressure shell includes an enlarged diameter upper shell portion and a reduced diameter lower shell portion, a conical transistion member connecting said shell portions, said baffle plate cooperating with the internal surface of said transition member to form said settling chamber.
 7. The organization of claim 6 in which the lower end of said baffle plate is sealedly connected to said pressure shell at the juncture of said transition member and said lower shell portion.
 8. The organization of claim 4 in which said cylindrical plate is attached to said pressure shell and including a second annular member attached to said cylindrical baffle in concentrically spaced relation to said cylindrical plate and cooperating therewith to define a tortuous fluid path between said settling chamber and said downcomer passage.
 9. The organization of claim 4 in which said second annular member is angular in section and telescopically encloses said cylindrical plate. 